I. Field of the Invention
This invention relates to a rotor shaft construction for a fluid pump or the like and, in particular, to a shaft construction which utilizes a corrosion resistant ferrule mounted to the end of the carbon steel rotor shaft.
II. Description of the Prior Art
In a fluid pump assembly, rotational torque is transferred from the drive motor to the fluid impeller through a rotor shaft extending from the stator winding within the motor housing. Typically, the impeller is housed in a detachable pump housing for ease of repair or replacement of either the motor or the pump. For this reason a fluid seal must be provided to prevent leakage past the rotor shaft extending into the pump housing. Any sealing means may be utilized; however, typically a face seal, combining a carbon-based inner ring which rotates with the shaft and a ceramic outer ring which is stationary, are utilized in modern motor/pump assemblies. Conventional rubber seals also provide an inexpensive method of sealing about the rotor shaft.
Because of the environment within which such pumps are utilized, corrosion between the carbon seal ring and the full carbon shafts utilized in past known pump motors is a prevalent problem. This corrosion of the carbon shaft can result in a loss of seal integrity, causing leakage past the shaft and possibly into the electric motor. In the case of a rubber seal the continuous rotational motion of the shaft against the seal can cause the seal to become worn, resulting in leakage. Wear on the seal is particularly prevalent when a full carbon steel shaft is utilized. In order to reduce corrosion of the shaft and wear on the sealing means, the extrinsic end of the shaft has been formed of stainless steel polished to reduce friction. Typically, the stainless steel rod is inertia welded to the carbon steel shaft. However, other means, such as a threaded engagement, have been utilized to attach the stainless portion of the shaft. Although a full stainless steel rotor shaft is possible, the cost of such an arrangement make it prohibitive. Thus, the carbon steel main shaft with the stainless steel end portion provides the necessary strength while reducing wear on the sealing elements in contact with the shaft. Still, shaft constructions which further reduce production costs are continuously sought.